High-conductivity organic silica gel and preparation process thereof

Abstract

The invention relates to the field of conductive silica gel, and discloses high-conductivity organic silica gel and a preparation process thereof.The high-conductivity organic silica gel is prepared from 100 parts of vinyl-terminated polydimethylsiloxane, 5-15 parts of hydrogen-containing silicone oil cross-linking agent, 0.1-0.5 part of platinum catalyst, 20-40 parts of conductive filler, 0.5-2 parts of inhibitor methyl butynol and 1-3 parts of epoxy silane coupling agent; the conductive filler comprises a composite filler of silver nanowires and nickel particles, and a polydopamine-coated carbon nanotube, the mass ratio of the silver nanowires to the nickel particles is 3: 1-5: 1, and the polydopamine-coated carbon nanotube accounts for 10-20% of the total mass of the conductive filler. Nickel particles are anchored to siloxane chain segments through mechanical stirring, silver nanowires are driven to grow along the nickel surface in a bridging mode through the ultrasonic cavitation effect, a three-dimensional framework with the porosity of 35 + / -5% and the percolation threshold value of 12.5 vol% is formed, and therefore the effect that compared with organic silica gel prepared through a single silver filler system, the performance of the organic silica gel is greatly improved is achieved. And the conductive stability of the organic silica gel prepared from the conductive filler is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of conductive silica gel, in particular to highly conductive organic silica gel and a preparation process thereof. Background Art

[0002] Conductive silicone is a functional polymer material that has both electrical conductivity and rubber elasticity. It not only has the characteristics of ordinary silicone such as high and low temperature resistance, aging resistance, and good insulation, but also has good conductivity due to the uniform dispersion of conductive fillers. It can achieve functions such as electrostatic release and electromagnetic shielding. It has a wide range of applications. In the field of electronics and electrical appliances, it can be used to make buttons, connectors, electromagnetic shielding parts, etc. to ensure stable operation of equipment; in the automotive industry, it is suitable for sensor seals, shock-proof conductive parts of electronic components, etc.; in the aerospace field, it can be used for conductive sealing components of precision instruments to meet the conductivity and protection needs in harsh environments.

[0003] Existing conductive silicone uses a single filler system (such as pure silver powder), which has few contact points between particles and is easily damaged by stress, resulting in a high percolation threshold and a resistance fluctuation rate of >15% under dynamic stretching, which leads to unstable conductive performance of the product. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the present invention provides a highly conductive organic silica gel and a preparation process thereof, which solves the problem that the conductive performance of the product is unstable due to the use of a single filler system in the existing conductive silica gel.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution: a highly conductive organic silica gel comprises the following components in parts by weight: 100 parts of vinyl-terminated polydimethylsiloxane, 5-15 parts of a hydrogenated silicone oil crosslinker, 0.1-0.5 parts of a platinum catalyst, 20-40 parts of a conductive filler, 0.5-2 parts of an inhibitor, methylbutynol, and 1-3 parts of an epoxy silane coupling agent; the conductive filler comprises a composite filler of silver nanowires and nickel particles and polydopamine-coated carbon nanotubes, wherein the mass ratio of the silver nanowires to the nickel particles is between 3:1 and 5:1, the polydopamine-coated carbon nanotubes account for 10-20% of the total mass of the conductive filler, the silver nanowires form a three-dimensional skeleton network by bridging the nickel particles, and the polydopamine-coated carbon nanotubes are dispersed in the network gaps through interfacial adhesion.

[0006] According to the technical solution, 100 parts of vinyl silicone oil with a viscosity of 5k-15kcps and a vinyl content of 0.05-0.15 mol% is used as a matrix, and 5-15 parts of hydrogenated silicone oil with a hydrogen content of 0.8-1.5 wt% is premixed under a vacuum of ≤-0.09 MPa for 30-60 minutes. Subsequently, 0.1-0.5 parts of a platinum catalyst and 0.5-2 parts of a methylbutynol inhibitor are added. The inhibitor is vulcanized by platinum-vinyl coordination, and the induction period is extended to 30-50 minutes. Subsequently, 20-50 nm × 10-50 μm silver nanowires and 0.5-2 μm spherical nickel particles are mixed in a ratio of 3:1-5:1, and a three-dimensional network with a porosity of 30-50% is formed by stirring and ultrasonication. Then, a carbon nanotube:polydopamine coated carbon tube with a ratio of 2:1-5:1 is added at 1000-2000 rpm and 500-1500 s. -1 The gaps are filled under certain conditions to form a bonding interface, and finally the system is cured by gradient vulcanization. Pre-vulcanization reduces the Si-H / vinyl reactivity to >80%, and final vulcanization increases the crosslinking density to a crosslinking point of ≤5nm. The final product has a volume resistivity of ≤0.05Ω·cm and a tensile strength of ≥2.5MPa. When the silver-nickel ratio is 4:1 and the polydopamine-coated carbon nanotubes account for 15%, the 10% strain resistance fluctuation is <5%, and after aging at 85℃ / 85%RH for 500h, the interfacial bonding energy retains 91.8%, which is superior to that of a single filler system.

[0007] Preferably, in the conductive filler: the silver nanowire has a diameter of 20-50 nm and a length of 10-50 μm, the nickel particles are spherical with an average particle size of 0.5-2 μm, the polydopamine-coated carbon nanotubes have a continuous coating layer of 5-20 nm, and the surface hydroxyl content is ≤3 at%.

[0008] Preferably, the mass ratio of carbon nanotubes to polydopamine in the polydopamine-coated carbon nanotubes is between 2:1 and 5:1, and the uniformity deviation of the coating thickness along the axial direction of the carbon nanotubes is ≤15%.

[0009] Preferably, the viscosity of the vinyl-terminated polydimethylsiloxane is 5000-15000 cps, and the vinyl content is 0.05-0.15 mol%; the hydrogen content of the hydrogen-containing silicone oil is 0.8-1.5 wt%, and the molecular weight is 2000-5000 g / mol.

[0010] Preferably, the epoxy silane coupling agent is γ-glycidyloxypropyltrimethoxysilane, and the addition amount thereof is 1.5-2.5 parts.

[0011] Preferably, the preparation process of highly conductive organic silica gel comprises the following steps: S1. Mix vinyl-terminated polydimethylsiloxane and hydrogenated silicone oil crosslinker under vacuum degree ≤-0.09 MPa for 30-60 min; S2. Add platinum catalyst and methylbutynol, and stir and disperse at 500-800 rpm for 20-40 min; S3. Add conductive fillers step by step: first add nickel particles and mechanically stir at 800-1200 rpm for 10 min, then add silver nanowires and ultrasonicate at 500-1000 W and 20-40°C for 30-60 min, and finally add polydopamine-coated carbon nanotubes and mechanically stir at 1000-2000 rpm for 2-4 h; S4. After vacuum degassing, inject into the mold and adopt gradient temperature vulcanization process. Pre-vulcanize at 60-80℃ for 30min, then heat to 100-120℃ for final vulcanization for 1-2h.

[0012] Preferably, when silver nanowires are added to S3 for ultrasonic treatment, the ultrasonic working cycle is 2 seconds / pause 1 second, and the ultrasonic power density is controlled at 50-100 W / cm 3 , the total energy input range is 150-300kJ / kg.

[0013] Preferably, when adding polydopamine-coated carbon nanotubes to S3 and mechanically stirring, the temperature in the stirring tank is controlled at 25-35°C by jacket circulating water, and the shear rate is simultaneously applied at 500-1500s -1 Flow field control, shear stress range is 20-50Pa.

[0014] Preferably, in S4, a constant pressure of 0.5-1 MPa is applied in the pre-vulcanization stage, and a nitrogen protective environment is introduced in the final vulcanization stage, wherein the nitrogen flow rate is 5-10 L / min, and the vulcanization pressure is increased to 1.5-2 MPa.

[0015] Preferably, in S4, the degassing vacuum degree is ≤-0.095 MPa, the degassing time is 30-60 minutes, and the viscosity of the rubber material after degassing is controlled to be 8000-20000 cps.

[0016] The present invention provides a highly conductive organic silica gel and a preparation process thereof. It has the following beneficial effects: 1. The present invention uses mechanical stirring to anchor nickel particles to siloxane segments and drives silver nanowires to grow along the nickel surface through ultrasonic cavitation effect, forming a three-dimensional skeleton with a porosity of 35±5% and a percolation threshold of 12.5vol%. Intermittent ultrasound reduces the wire breakage rate to <5%, and the spherical structure of the nickel particles reduces the contact resistance to <10 -8 Ω·m 2, volume resistivity ≤ 0.05Ω·cm, resistance fluctuation rate under 10% strain < 5%, thereby achieving the effect of improving the conductive stability of organic silicone gel prepared by a single silver filler system and organic silicone gel prepared by conductive fillers.

[0017] 2. The present invention forms a 5-20 nm uniform coating layer through oxidative polymerization of dopamine in a pH = 8.5 buffer solution. The catechol group and the silanol group form a hydrogen bond / covalent bond composite interface, and the van der Waals aggregation is destroyed by high-speed shear, so that the carbon nanotubes are embedded in the network gap and the density of the conductive path is increased. As a result, after aging the organic silica gel at 85°C / 85% RH for 500 hours, the interfacial binding energy decreases by only 8.2%, the resistivity change rate is <7.5%, and the debonding area is <5%, which enhances the environmental stability of the organic silica gel compared to directly adding carbon nanotubes.

[0018] 3. The present invention completes 80% Si-H addition reaction through pre-vulcanization to fix the conductive network topology, while the final vulcanization inhibits thermal expansion distortion and increases the cross-linking density to 5×10 -4 mol / cm 3 (spacing ≤ 5nm), high pressure suppresses silver lattice strain <0.15%, nitrogen blocks free radical side reactions, and the free radical concentration drops by 90%, which makes the organic silicone tensile strength ≥3.5MPa, elongation at break ≥320%, resistivity change rate after aging for 1000h <3%, and residual stress <0.3MPa, achieving synergistic enhancement of mechanical and electrical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a process flow chart of the preparation process of the highly conductive organic silica gel proposed in the present invention. DETAILED DESCRIPTION

[0020] The following will clearly and completely describe the technical solution of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0021] Please see the attached Figure 1, highly conductive organic silicone, including the following components in parts by mass: 100 parts of vinyl-terminated polydimethylsiloxane, 5-15 parts of hydrogenated silicone oil crosslinking agent, 0.1-0.5 parts of platinum catalyst, 20-40 parts of conductive filler, 0.5-2 parts of inhibitor methyl butynol, and 1-3 parts of epoxy silane coupling agent; the conductive filler includes a composite filler of silver nanowires and nickel particles, and polydopamine-coated carbon nanotubes, wherein the mass ratio of silver nanowires to nickel particles is between 3:1 and 5:1, and the polydopamine-coated carbon nanotubes account for 10-20% of the total mass of the conductive filler. The silver nanowires form a three-dimensional skeleton network by bridging the nickel particles, and the polydopamine-coated carbon nanotubes are dispersed in the network gaps through interfacial adhesion.

[0022] Specifically, first, 100 parts of vinyl-terminated polydimethylsiloxane (viscosity 5000-15000 cps, vinyl content 0.05-0.15 mol%) is used as a matrix, and 5-15 parts of hydrogenated silicone oil crosslinker (hydrogen content 0.8-1.5 wt%) are premixed under a vacuum degree of ≤-0.09 MPa for 30-60 minutes to achieve uniform dispersion through hydrogen bonding between molecular chains; then, 0.1-0.5 parts of platinum catalyst (Karstedt catalyst) and 0.5-2 parts of methylbutynol inhibitor are added, and Pt 0 The coordination with vinyl initiates the addition vulcanization reaction, while the inhibitor slows down the reaction rate by chelating free Pt, avoiding local overheating and filler sedimentation. The gradient dispersion process design of the conductive filler is based on the percolation theory: silver nanowires (20-50nm×10-50μm) and nickel particles (spherical, 0.5-2μm) are compounded in a mass ratio of 3:1-5:1, and the nickel particles are evenly anchored to the siloxane chain segments by mechanical stirring at 800-1200rpm, and then heated at 20-40℃ for 50 min. Ultrasonic treatment at 0-1000W for 30-60min induced the growth of silver nanowires along the surface of nickel particles, forming a three-dimensional skeleton network with a porosity of 30-50%, and the percolation threshold was reduced to 12vol%. Polydopamine-coated carbon nanotubes (carbon nanotube to polydopamine mass ratio of 2:1-5:1) formed a hydrogen bond / covalent bond composite interface with the silicone rubber matrix through the catechol group of polydopamine. Under high-speed shear of 1000-2000rpm (shear rate of 500-1500s -1 ) fill the network gap and simultaneously increase the density of the conductive path (≥10 4 strips / mm 2) and interface bonding strength; the pre-vulcanization stage (0.5-1MPa) promotes more than 80% addition reaction between Si-H and vinyl groups, fixing the topological structure of the conductive network; the final vulcanization stage (1.5-2MPa, nitrogen protection) eliminates residual stress and enhances the cross-linking density (cross-linking point spacing ≤5nm), making the volume resistivity ≤0.05Ω·cm and the tensile strength ≥2.5MPa. When the silver / nickel mass ratio is 4:1 and the polydopamine-coated carbon nanotubes account for 15%, the resistance fluctuation of the conductive network is less than 5% under 10% strain, and the interfacial binding energy decreases by only 8.2% after aging at 85℃ / 85%RH for 500 hours (XPS characterization of CO-Si bond retention rate >90%). Under the same conditions, the resistance fluctuation of the single filler system is >15%, and the binding energy decreases by >30%, which is better than the single filler system.

[0023] In the conductive filler, the silver nanowire has a diameter of 20-50nm and a length of 10-50μm, the nickel particles are spherical and have an average particle size of 0.5-2μm, the polydopamine-coated carbon nanotubes have a continuous coating layer of 5-20nm, and the surface hydroxyl content is ≤3at%.

[0024] Specifically, in the preparation and compounding process of conductive fillers, the parameter design and process control are based on the principles of microstructure regulation and interface optimization: silver nanowires are synthesized by a solvent thermal method. By regulating the molar ratio of silver nitrate to polyvinyl pyrrolidone (1:3 to 1:5) and the reaction temperature (120-160°C), high aspect ratio nanowires (aspect ratio ≥ 500) with a diameter of 20-50 nanometers and a length of 10-50 microns are obtained. This size range can ensure that the silver nanowires are effectively bridged in the silicone rubber matrix and avoid excessive entanglement; nickel particles are prepared by a liquid phase reduction method, using nickel sulfate as a precursor and hydrazine hydrate as a reducing agent, controlling the pH value to 9-11 and the reaction time to 2-4 hours, to form spherical particles with an average particle size of 0.5-2 microns (sphericity ≥ 0.9). Their geometric characteristics can reduce the contact resistance between particles (<10 -8 Ω·m 2); The preparation of polydopamine-coated carbon nanotubes involves an interfacial self-assembly process: carboxylated carbon nanotubes (-COOH content 3-5wt%) are dispersed in tris (hydroxymethylaminomethane) hydrochloride buffer (pH = 8.5), dopamine hydrochloride is added (carbon nanotube to dopamine mass ratio 2:1-5:1), and oxidative polymerization is carried out at 25-35°C for 12-24 hours to form a 5-20 nanometer continuous coating layer through π-π conjugation and hydrogen bonding. XPS analysis shows that the surface hydroxyl content after coating is ≤3 atomic percent, which can inhibit carbon The nanotubes aggregated and enhanced the chemical bonding with the siloxane matrix (FTIR showed that the intensity of the CO-Si characteristic peak increased by 2-3 times); when the mass ratio of silver nanowires to nickel particles was 4:1, SEM observation showed that the composite filler formed a three-dimensional interpenetrating network with a porosity of 35±5% in the silicone rubber, and the conductive percolation threshold dropped to 12.5vol%, which is lower than that of the single silver filler system (threshold>22vol%); the introduction of polydopamine-coated carbon nanotubes (accounting for 15%) increased the interfacial binding energy to 1.8J / m through stripping experiments. 2 , the sample was subjected to 500h aging test under 85℃ / 85%RH conditions, and the volume resistivity change rate was <7.5%, showing excellent interface stability.

[0025] The mass ratio of carbon nanotubes to polydopamine in the polydopamine-coated carbon nanotubes is between 2:1 and 5:1, and the uniformity deviation of the coating thickness along the axial direction of the carbon nanotubes is less than or equal to 15%.

[0026] Specifically, the mass ratio of carbon nanotubes to dopamine is controlled within the range of 2:1 to 5:1. When the mass ratio is less than 2:1, the coating layer is prone to island discontinuity. When the mass ratio is greater than 5:1, the coating layer is too thick to block the conductive path. Oxygen is introduced at 25-35°C (flow rate 10-20 ml / min) to initiate an oxidative polymerization reaction. Through the π-π conjugation effect of the dopamine catechol group, it is preferentially adsorbed on the defect sites of the carbon nanotubes and undergoes free radical polymerization along the axial direction. The reaction time is controlled within 12-24 hours. Then, a transmission electron microscope is used to measure 50 measurement points to form a continuous coating layer with a thickness of 5-20 nm and a uniformity deviation of ≤15%. When the mass ratio of carbon nanotubes to dopamine is 3:1, the polymerization Dopamine forms a strong interfacial bond with the silanol groups of the silicone rubber matrix through hydrogen bonds. Atomic force microscopy measurements show a binding energy of 2.1 joules per square meter. X-ray photoelectron spectroscopy analysis shows that the residual hydroxyl content in the coating layer is ≤3at%, and the filler distribution uniformity index after aging is >0.85, which can inhibit the migration of carbon nanotubes. After aging for 500 hours at 85°C / 85% relative humidity, scanning electron microscopy observations show that the coating thickness change rate is <8%, and the interface debonding area accounts for <5%, which is better than the uncoated carbon nanotube system (debonding area >30% under the same conditions). This parameter range ensures that the composite material has a conductive path retention rate of ≥95% under a tensile strain of 10%, while maintaining a tensile strength of ≥2.8 MPa.

[0027] The viscosity of the vinyl-terminated polydimethylsiloxane is 5000-15000 cps, and the vinyl content is 0.05-0.15 mol%. The hydrogen content of the hydrogen-containing silicone oil is 0.8-1.5 wt%, and the molecular weight is 2000-5000 g / mol.

[0028] Specifically, octamethylcyclotetrasiloxane is used as a monomer and tetramethylammonium hydroxide is used as a catalyst. The reaction is carried out at 80-120°C for 4-8 hours. The vinyl content is precisely controlled by adjusting the amount of vinyl end-capping agent (vinyltrimethoxysilane) added (0.5-1.5 mol%). At the same time, molecular distillation technology (temperature 150-180°C, vacuum degree ≤5Pa) is used to regulate the polymer molecular weight so that the viscosity is adapted to the filler dispersion requirements. Low viscosity is conducive to shear dispersion, and high viscosity inhibits filler sedimentation. By Dichlorosilane and dimethyldichlorosilane were mixed in a molar ratio of 1:5-1:8, hydrolyzed in a pH 6-7 aqueous solution (temperature 0-5°C), and vacuum dehydrated at 120-150°C. After polycondensation, the hydrogen content was monitored by gas chromatography. When the hydrogen content was less than 0.8%, the crosslinking density was insufficient (crosslinking point spacing > 10 nm), and when it was > 1.5%, the vulcanization was too fast (gel time < 5 minutes). When the vinyl content was 0.1 mol% and the hydrogen content was 1.2%, the crosslinking density of the vulcanized rubber reached 4.5×10 -4 The synergistic effect of the platinum catalyst and the inhibitor (methyl butynol) extends the vulcanization induction period to 30-50 minutes, providing sufficient time for the network construction of the conductive filler.

[0029] The epoxy silane coupling agent is γ-glycidyloxypropyltrimethoxysilane, and the added amount thereof is 1.5-2.5 parts.

[0030] Specifically, the epoxy silane coupling agent generates silanol by hydrolysis of methoxy groups, which reacts with the hydroxyl groups on the surface of the conductive filler to form Si-OC or Si-O-Ag covalent bonds. FTIR shows that 1050 cm -1 The intensity of the Si-O-Si characteristic peak at the interface is increased by 2.5 times; at the same time, its epoxy group (-CH2-O-CH2-) undergoes a ring-opening addition reaction with the vinyl group of the vinyl-terminated polydimethylsiloxane during the vulcanization process to form a stable COC cross-linked network. When the addition amount is less than 1.5 parts, the coupling agent cannot completely cover the filler surface. The XPS atomic concentration analysis shows that the coverage is less than 70%. The atomic force microscopy peeling test shows that the interface binding energy is ≤1.2J / m 2 When the addition amount is greater than 2.5 parts, the excess coupling agent self-polymerizes to form a non-cross-linked layer 5-10 nm thick, which blocks the conductive path and reduces the tensile strength (less than 2.0 MPa).

[0031] The preparation process of highly conductive organic silica gel includes the following steps: S1. Mix vinyl-terminated polydimethylsiloxane and hydrogenated silicone oil crosslinker under vacuum degree ≤-0.09 MPa for 30-60 min; S2. Add platinum catalyst and methylbutynol, and stir and disperse at 500-800 rpm for 20-40 min; S3. Add conductive fillers step by step: first add nickel particles and mechanically stir at 800-1200 rpm for 10 min, then add silver nanowires and ultrasonicate at 500-1000 W and 20-40°C for 30-60 min, and finally add polydopamine-coated carbon nanotubes and mechanically stir at 1000-2000 rpm for 2-4 h; S4. After vacuum degassing, inject into the mold and adopt gradient temperature vulcanization process. Pre-vulcanize at 60-80℃ for 30min, then heat to 100-120℃ for final vulcanization for 1-2h.

[0032] Specifically, in S1, vinyl-terminated polydimethylsiloxane and a hydrogenated silicone oil crosslinker are mixed under a vacuum degree of ≤-0.09 MPa for 30-60 minutes, and the dissolved oxygen and volatile small molecules in the matrix are removed by the vacuum environment, wherein the residual bubble volume fraction is ≤0.05%, and at the same time, hydrogen bond pre-crosslinking of the siloxane segments is promoted to provide a uniform matrix for subsequent vulcanization; After adding platinum catalyst and methyl butynol to S2, stirring at a medium speed of 500-800 rpm for 20-40 minutes, an activation center is formed by the coordination of platinum-vinyl (UV-Vis detection of Pt 0 -L coordination peak red shift 15nm), while the inhibitor chelates free platinum ions (binding constant K = 10 3 -10 4 L / mol) to extend the vulcanization induction period to 30-50 minutes (determined by oscillatory rheometer) to avoid premature gelation leading to uneven distribution of fillers; In S3, nickel particles were mechanically stirred at 800-1200 rpm for 10 min, and the shear force field (shear rate 300-500 s-1) was used to uniformly anchor the nickel particles to the siloxane segments, forming primary conductive nodes (contact resistance <10 -7 Ω·m 2); silver nanowires were ultrasonically treated at 500-1000 watts, and the microjets generated by the cavitation effect drove the silver nanowires to bridge along the surface of nickel particles (SEM showed a bridging density of ≥8 per particle), constructing a three-dimensional skeleton network with a porosity of 30-50%; polydopamine-coated carbon nanotubes were dispersed at a high-speed shear of 1000-2000 rpm for 2-4 hours, using the catechol groups of polydopamine to form a hydrogen-covalent bond composite interface with the silanol groups, and FTIR showed a 1020 cm -1 The Si-OC peak intensity at the junction of the 1.5×10 4 bars / square millimeter); In S4, the pre-curing stage promotes 60-80% of Si-H to react with vinyl. 1 H-NMR monitored the reduction in Si-H peak area, preliminarily fixing the conductive network topology. The final vulcanization stage completed the remaining cross-linking reaction, and high voltage was used to suppress network distortion. XRD showed that the silver lattice strain was less than 0.15%, ultimately obtaining a silicone rubber with a volume resistivity ≤ 0.05 ohm·cm and a tensile strength ≥ 3.0 MPa.

[0033] When silver nanowires were added to S3 for ultrasonic treatment, the ultrasonic working cycle was 2 seconds / pause was 1 second, and the ultrasonic power density was controlled at 50-100 W / cm 3 , the total energy input range is 150-300kJ / kg.

[0034] Specifically, by adopting an intermittent mode of 2 seconds of ultrasound / 1 second pause, the microjets generated by the collapse of cavitation bubbles can be periodically released, ensuring the effective deagglomeration of silver nanowires while avoiding wire breakage caused by continuous ultrasound. SEM statistics show that the wire breakage rate in the intermittent mode is less than 5%, while that in the continuous mode is greater than 15%; when the power density is less than 50W / cm 3 When the cavitation threshold was not broken (acoustic pressure < 0.3 MPa), laser particle size analysis showed that D50 > 5 μm, which meant that the silver nanowire aggregates could not be effectively dispersed. 3 It induces local high temperature (>60℃), the storage modulus G' detected by rheometer increases abnormally by 20%, the siloxane matrix is ​​pre-crosslinked, and XPS shows that the Ag2O content increases from 0.8% to 3.5%, and the oxidation of silver nanowires is aggravated; when the total energy input is less than 150kJ / kg, the filler dispersion index (DDI) is less than 0.75, and the conductive network has more than 20% of isolated island areas; when the energy is greater than 300kJ / kg, the surface defect density of silver nanowires increases (HR-TEM observation of dislocation density>10 10 / cm 2 ), resistivity rebound> 15%; at power density 80W / cm 3Under the condition of total energy of 240kJ / kg, silver nanowires are evenly anchored on the surface of nickel particles in the form of 3-5 wires / cluster (coverage >90%), forming a three-dimensional conductive network with a porosity of 35±3%, which reduces the percolation threshold to 12.8vol%. At the same time, the aspect ratio of the wire is maintained at >480, ensuring the comprehensive performance of resistivity ≤0.05Ω·cm and tensile strength ≥3.2MPa at the lowest energy consumption.

[0035] When polydopamine-coated carbon nanotubes are added to S3 and mechanically stirred, the temperature in the stirring tank is controlled at 25-35°C by jacket circulating water, and the shear rate is simultaneously applied at 500-1500s -1 Flow field control, shear stress range is 20-50Pa.

[0036] Specifically, the temperature in the reactor is precisely controlled by the jacket circulating water system (water temperature set at 20℃±1℃, flow rate 5-10L / min). When the temperature is less than 25℃, the viscosity of the silicone rubber matrix increases, resulting in uneven shear force distribution. CFD simulation shows that the local shear rate deviation is greater than 30%; and the temperature greater than 35℃ will trigger thermal oxidative degradation of the polydopamine coating. TGA shows that the weight loss rate increases from 0.8% to 2.5%, causing the surface hydroxyl content to rise to greater than 4at% and weakening the interface bonding; the yield stress threshold of the carbon nanotube agglomerates is determined to be 18-22Pa by rheological amplitude scanning, so the shear stress lower limit is designed to be greater than 20Pa to destroy the agglomeration dominated by van der Waals forces, and the agglomerate size is reduced from the initial 5-10μm to 1-2μm. At the same time, the upper limit is ≤50Pa to avoid excessive shearing and peeling of the polydopamine coating; a double-layer paddle stirrer (upper inclined blade paddle, lower turbine paddle) is used at 500-1500s -1 An axial-radial composite flow field is formed within the velocity range, causing carbon nanotubes to be embedded in the gaps of the silver-nickel network in the three-dimensional direction; the tensile flow induced by the shear flow field promotes the dynamic hydrogen bond recombination between the polydopamine catechol groups and the siloxane segments, while the mechanochemical effect activates the covalent grafting of silanol groups and dopamine quinone structures; at 30℃ / 1000s -1 Under these conditions, the carbon nanotube-matrix interface bonding energy reaches 2.3 J / m 2 After 100 cycles of 10% stretching, the resistance fluctuation rate of the composite material is less than 3%, which is higher than that of the unoptimized process (fluctuation rate > 12%). This parameter combination has been verified by the response surface methodology and can simultaneously achieve a conductive path density of ≥ 1.2×10 4 strips / mm 2 (μ-CT three-dimensional reconstruction) and synergistic optimization of tensile strength ≥3.5MPa (ISO527 standard).

[0037] In S4, a constant pressure of 0.5-1 MPa is applied in the pre-vulcanization stage, and a nitrogen protective environment is introduced in the final vulcanization stage, wherein the nitrogen flow rate is 5-10 L / min, and the vulcanization pressure is increased to 1.5-2 MPa.

[0038] Specifically, in the pre-vulcanization stage, constant pressure is applied at 60-80°C to align the siloxane molecular chains through mechanical compression. At the same time, the pressure drives the platinum catalyst-vinyl complex to come into close contact, so that the addition reaction of Si-H and vinyl reaches more than 80% completion. 1 H-NMR monitors the Si-H characteristic peak area decay rate; when the pressure is lower than 0.5 MPa, the matrix fluidity is too high, resulting in distortion of the silver-nickel conductive network due to gravity sedimentation (porosity deviation observed by SEM > 10%), while when it is higher than 1 MPa, crosslinking points are locked prematurely (crosslinking density > 3×10 -4 mol / cm 3 ), hindering the stress release in the final vulcanization stage; in the final vulcanization stage, the temperature is raised to 100-120℃ and the pressure is increased to suppress the volume change caused by thermal expansion by high pressure (the thermal expansion coefficient is from 5×10 -4 / ℃ down to 2×10 -4 / ℃), which promoted the complete reaction of residual vinyl groups. FTIR showed 1630cm -1 The C=C peak at the bottom of the column disappeared, and the nitrogen protection blocked the free radical oxidation side reaction (the free radical concentration was reduced by 90% by electron paramagnetic resonance). At the same time, the high-speed nitrogen flow (5-10 L / min) took away the volatile small molecules. The residual amount of siloxane oligomers was <0.1% by GC-MS, and the cross-linking density was 5×10 -4 mol / cm 3 , improve the regularity of the cross-linking network; under the conditions of 1.8 MPa pressure and 8 liters / minute nitrogen, the internal residual stress of the vulcanized rubber was measured by photoelasticity method to drop to <0.3 MPa, and the volume resistivity was ≤0.04Ω·cm (four-probe method), and after aging at 85℃ / 85% RH for 1000 hours, the resistivity change rate was <3%, compared with the non-nitrogen protection system >12%. This process achieves the coordinated optimization of conductive network stability and mechanical properties (tensile strength ≥3.5 MPa, elongation at break ≥320%) through the ternary control of pressure-temperature-atmosphere.

[0039] In S4, the degassing vacuum degree is ≤-0.095MPa, the degassing time is 30-60 minutes, and the viscosity of the rubber after degassing is controlled at 8000-20000cps.

[0040] Specifically, by reducing the gas phase partial pressure to promote bubble expansion, when the vacuum degree is insufficient, bubbles with a diameter greater than 50μm cannot be effectively ruptured, while excessive vacuum causes the volatilization of low-molecular-weight components of silicone, destroying the molecular weight distribution of the matrix; when the initial viscosity of the rubber material before degassing is greater than 30,000 centipoise, the bubble migration resistance is too large, and when the viscosity is less than 8,000 centipoise, the filler sedimentation rate observed by X-ray real-time imaging is greater than 0.1mm / min. This parameter combination makes the internal defect size of the material ≤10μm after vulcanization (micro-CT analysis), the volume resistivity fluctuation rate less than 2% (four-probe multi-point test), and the small-angle X-ray scattering shows an orientation factor greater than 0.75, which can avoid the orientation disorder of silver nanowires caused by excessive degassing.

[0041] Example 1: High conductivity optimization 1. Ingredients (parts by mass): vinyl-terminated polydimethylsiloxane: 100 parts, hydrogenated silicone oil crosslinker: 10 parts, platinum catalyst: 0.3 parts, methylbutynol inhibitor: 1.2 parts, silver nanowires: 24 parts, nickel particles: 6 parts, polydopamine-coated carbon nanotubes: 5.4 parts, epoxy silane coupling agent: 2 parts.

[0042] 2. Preparation process: S1: Vinyl-terminated polydimethylsiloxane and hydrogenated silicone oil crosslinker were mixed under vacuum of -0.095 MPa for 30 minutes, and the base viscosity dropped to 9000 cps. S2: Add catalyst and inhibitor, stir at 500 rpm for 20 minutes, S3: Add nickel particles and mechanically stir at 800 rpm for 10 minutes, then add silver nanowires and ultrasonically treat at a power of 500 W and a temperature of 20°C for 30 minutes. Finally, add polydopamine-coated carbon nanotubes and high-speed shear at 1000 rpm for 2 hours.

[0043] S4: Pre-vulcanize at 60℃ for 30min, then heat to 100℃ for final vulcanization for 1h.

[0044] 3. Performance: Volume resistivity: 0.035Ω·cm, Tensile strength: 3.6MPa, 10% strain resistance fluctuation rate: 4.2%, Resistance change after aging at 85℃ / 85%RH for 500h: 5.8%.

[0045] 4. Control experimental group: 1. Ingredients (parts by mass): The conductive filler is silver nanowires only: 30 parts, without nickel and polydopamine-coated carbon nanotubes. Other ingredients are the same as in Example 1.

[0046] 2. Preparation process: S3 omits nickel particle dispersion and ultrasonic bridging steps, and directly mixes silver nanowires. S4 The final sulfurization pressure is reduced to 1.0 MPa, without gradient pressurization. Others are the same as in Example 1.

[0047] 3. Performance: Volume resistivity: 0.28Ω·cm, Tensile strength: 1.7MPa, 10% strain resistance fluctuation rate: 22%, Resistance change after aging: 35%.

[0048] 5. Performance comparison: Example 2: High strain stability 1. Ingredients (mass composition): Vinyl-terminated polydimethylsiloxane: 100 parts, hydrogenated silicone oil crosslinker: 10 parts, platinum catalyst: 0.3 parts, methylbutynol inhibitor: 1.2 parts, epoxy silane coupling agent: 2 parts, silver nanowires: 25 parts, nickel particles: 5 parts, polydopamine-coated carbon nanotubes: 7 parts, hydrogenated silicone oil crosslinker: 12 parts.

[0049] 2. Preparation process: S1. Mix vinyl-terminated polydimethylsiloxane and hydrogenated silicone oil crosslinker under vacuum of -0.095 MPa for 45 minutes; S2. Add platinum catalyst and methyl butynol, and stir and disperse at 650 rpm for 30 minutes; S3, adding conductive fillers step by step: first add nickel particles, stir mechanically at 1000 rpm for 10 min, then add silver nanowires, and perform ultrasonic treatment at a power of 750 W and a temperature of 30 ° C for 45 min, and finally add polydopamine-coated carbon nanotubes, stir mechanically at 1500 rpm for 3 h, and adjust the ultrasonic power density to 60 W / cm 3 ; S4. After vacuum degassing treatment, the product is injected into the mold and a gradient temperature rise vulcanization process is adopted. The product is pre-vulcanized at 70°C for 30 minutes, then heated to 110°C for final vulcanization for 1.5 hours, and the final vulcanization pressure is increased to 2.0 MPa.

[0050] 3. Performance: Volume resistivity: 0.045Ω·cm20% Strain resistance fluctuation rate: 6.8% Resistance change after 100 cycles of stretching: +3.5% Interface binding energy: 2.5J / m 2 4. Control experimental group: 1. Ingredients (parts by mass): 7 parts of pristine carbon nanotubes for conductive filler, without dopamine coating. Other ingredients are the same as those in Example 2.

[0051] 2. Preparation process: S3 omits the dopamine coating step and directly adds the original carbon nanotubes. Other steps are the same as those in Example 2.

[0052] 3. Performance: Volume resistivity: 0.063Ω·cm, 20% strain resistance fluctuation rate: 28%, Interface binding energy: 0.8J / m 2 .

[0053] 5. Performance comparison: Example 3: Application in high temperature and high humidity environment 1. Ingredients (mass composition): Vinyl-terminated polydimethylsiloxane: 100 parts, platinum catalyst: 0.3 parts, methylbutynol inhibitor: 1.2 parts, epoxy silane coupling agent: 2 parts, silver nanowires: 18 parts, nickel particles: 6 parts, polydopamine-coated carbon nanotubes: 3.6 parts, hydrogenated silicone oil crosslinking agent: 15 parts.

[0054] 2. Preparation process: S1. Mix vinyl-terminated polydimethylsiloxane and hydrogenated silicone oil crosslinker under vacuum of -0.095 MPa for 60 min. S2. Add platinum catalyst and methyl butynol, and stir and disperse at 800 rpm for 40 min. S3, adding conductive fillers step by step: first add nickel particles, mechanically stir at 1200 rpm for 10 min, then add silver nanowires, ultrasonicate at 1000 W and 40°C for 60 min, and finally add polydopamine-coated carbon nanotubes, mechanically stir at 2000 rpm for 4 h; S4. After vacuum degassing treatment, the product is injected into the mold and a gradient temperature vulcanization process is adopted. Pre-vulcanization is first performed at 80°C for 60 minutes, and then the temperature is raised to 120°C for final vulcanization for 2 hours. During the final vulcanization, the nitrogen flow rate is increased to 10L / min.

[0055] 3. Performance: 85℃ / 85%RH1000h resistance change: +2.7%, Crosslink density: 5.5×10 -4 mol / cm 3 , Glass transition temperature: -62°C.

[0056] 4. Control experimental group: 1. Ingredients (mass composition): The amount of hydrogenated silicone oil was reduced to 8 parts (hydrogen content 0.7 wt%), and the rest was the same as in Example 3.

[0057] 2. Preparation process: The final vulcanization pressure of S4 is 1.0 MPa (not pressurized), and the rest is the same as in Example 3.

[0058] 3. Performance: Resistance change after aging at 85℃ / 85%RH: 18%, Crosslink density: 3.2×10 -4 mol / cm 3 .

[0059] 5. Performance comparison: While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. Highly conductive organic silicone, characterized in that: The invention comprises the following components in parts by mass: 100 parts of vinyl-terminated polydimethylsiloxane, 5-15 parts of a hydrogenated silicone oil crosslinking agent, 0.1-0.5 parts of a platinum catalyst, 20-40 parts of a conductive filler, 0.5-2 parts of an inhibitor, methylbutynol, and 1-3 parts of an epoxy silane coupling agent; the conductive filler comprises a composite filler of silver nanowires and nickel particles and polydopamine-coated carbon nanotubes, wherein the mass ratio of the silver nanowires to the nickel particles is between 3:1 and 5:1, the polydopamine-coated carbon nanotubes account for 10-20% of the total mass of the conductive filler, the silver nanowires form a three-dimensional skeleton network by bridging the nickel particles, and the polydopamine-coated carbon nanotubes are dispersed in the network gaps through interfacial adhesion.

2. The highly conductive organic silica gel according to claim 1, characterized in that: In the conductive filler, the silver nanowire has a diameter of 20-50 nm and a length of 10-50 μm, the nickel particles are spherical and have an average particle size of 0.5-2 μm, the polydopamine-coated carbon nanotube has a continuous coating layer of 5-20 nm, and the surface hydroxyl content is ≤3 at%.

3. The highly conductive organic silica gel according to claim 1, characterized in that: The mass ratio of carbon nanotubes to polydopamine in the polydopamine-coated carbon nanotubes is between 2:1 and 5:1, and the uniformity deviation of the coating thickness along the axial direction of the carbon nanotubes is ≤15%.

4. The highly conductive organic silica gel according to claim 1, characterized in that: The viscosity of the vinyl-terminated polydimethylsiloxane is 5000-15000 cps, and the vinyl content is 0.05-0.15 mol%; the hydrogen content of the hydrogen-containing silicone oil is 0.8-1.5 wt%, and the molecular weight is 2000-5000 g / mol.

5. The highly conductive organic silica gel according to claim 1, characterized in that: The epoxy silane coupling agent is γ-glycidyloxypropyltrimethoxysilane, and the addition amount thereof is 1.5-2.5 parts.

6. The preparation process of highly conductive organic silica gel is characterized in that: The highly conductive organic silica gel according to any one of claims 1 to 5 comprises the following steps: S1. Mix vinyl-terminated polydimethylsiloxane and hydrogenated silicone oil crosslinker under vacuum degree ≤-0.09 MPa for 30-60 min; S2. Add platinum catalyst and methylbutynol, and stir and disperse at 500-800 rpm for 20-40 min; S3. Add conductive fillers step by step: first add nickel particles and mechanically stir at 800-1200 rpm for 10 min, then add silver nanowires and ultrasonicate at 500-1000 W and 20-40°C for 30-60 min, and finally add polydopamine-coated carbon nanotubes and mechanically stir at 1000-2000 rpm for 2-4 h; S4. After vacuum degassing treatment, inject into the mold and adopt gradient temperature vulcanization process. Pre-vulcanize at 60-80℃ for 30min, then heat to 100-120℃ for final vulcanization for 1-2h.

7. The process for preparing highly conductive organic silica gel according to claim 6, characterized in that: When silver nanowires were added to S3 for ultrasonic treatment, the ultrasonic working cycle was 2 seconds / pause was 1 second, the ultrasonic power density was controlled at 50-100 W / cm³, and the total energy input range was 150-300 kJ / kg.

8. The process for preparing highly conductive organic silica gel according to claim 6, characterized in that: When polydopamine-coated carbon nanotubes were added to S3 for mechanical stirring, the temperature in the stirring tank was controlled at 25-35°C by jacket circulating water, and a flow field control with a shear rate of 500-1500 s⁻¹ was simultaneously applied, and the shear stress range was 20-50 Pa.

9. The process for preparing highly conductive organic silica gel according to claim 6, wherein: In S4, a constant pressure of 0.5-1 MPa is applied in the pre-vulcanization stage, and a nitrogen protective environment is introduced in the final vulcanization stage, wherein the nitrogen flow rate is 5-10 L / min, and the vulcanization pressure is increased to 1.5-2 MPa.

10. The process for preparing highly conductive organic silica gel according to claim 6, characterized in that: In S4, the degassing vacuum degree is ≤-0.095MPa, the degassing time is 30-60 minutes, and the viscosity of the rubber after degassing is controlled at 8000-20000cps.

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